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High-grade gliomas, which include glioblastomas (GBMs) and anaplastic gliomas (AGs), are the most common malignant primary brain tumors in adults1 and are associated with poor survival despite maximal surgery, radiation, and chemotherapy.2–4 Bevacizumab, a humanized monoclonal antibody against vascular endothelial growth factor (VEGF), is frequently used to treat recurrent high-grade glioma (HGG). Bevacizumab monotherapy received accelerated approval for recurrent GBM by the United States Food and Drug Administration in 2009 on the basis of phase II clinical trials demonstrating response rates of 20%–26%, 6-month progression-free survival (PFS6) rates of 29%–42.6%, and median overall survival (OS) of 7.1–9.2 months.5,6 Phase II studies in recurrent AG suggest that bevacizumab plus irinotecan also has activity in this patient population with response rates of 55%–66% and PFS6 rates of 56%–61%.7,8 However, responses to bevacizumab are not durable, and some patients fail to benefit.9 Panobinostat is a potent, small-molecule inhibitor of classes I, II, and IV histone deacetylases (HDACs) with greater potency than vorinostat.10 HDAC inhibitors, including panobinostat, may inhibit angiogenesis by reducing VEGF secretion and modulating the expression of other VEGF family members via inhibition of HIF-1α.11–14 In addition, the SDF-1α/CXCR4 pathway has been implicated in bevacizumab resistance,15–17 and panobinostat depletes CXCR4 levels and signaling.18 A phase I study of panobinostat in combination with bevacizumab for recurrent HGG suggested that oral panobinostat 30 mg 3 times per week, every other week, can be safely combined with bevacizumab 10 mg/kg every other week.19 We conducted a multicenter, phase II trial of panobinostat in combination with bevacizumab in patients with recurrent GBM. We also examined the same combination of agents in patients with recurrent AG as an exploratory arm.

Bevacizumab is frequently used to treat recurrent high-grade gliomas, but responses are generally not durable. Panobinostat is a histone deacetylase inhibitor with anti-neoplastic and anti-angiogenic effects in glioma models and may work synergistically with bevacizumab. We conducted a multicenter phase II trial of panobinostat in combination with bevacizumab. Two cohorts were enrolled: one with recurrent glioblastoma (GBM) as the primary study and one with recurrent anaplastic glioma (AG) as the exploratory study. Patients received oral panobinostat 30 mg 3 x per week, every other week, in combination with bevacizumab 10 mg/kg every other week. The primary endpoint was PFS6 in the GBM cohort and the study was powered to discriminate between a 35% and 55% PFS6 rate (85% power at an alpha level of 0.07). At planned interim analysis, 13 of the first 21 patients accrued to the GBM cohort had progressed within 6 months of initiating study treatment. The GBM cohort did not meet criteria for continued accrual and was closed early. In the GBM cohort, PFS6 rate was 30.4%, median PFS 5 months, median OS 9 months. Accrual in the AG cohort continued to completion and a total of 15 patients were enrolled. In the AG cohort, PFS6 rate was 46.7%, median PFS 7 months, median OS 17 months. The most common grade 3 or 4 toxicities in the GBM arm were hypophosphatemia (12.5%), thrombocytopenia (12.5%), lymphopenia (8.3%), neutropenia (8.3%), and ALT elevation (8.3%). In the AG arm, the most common toxicities were thrombocytopenia (20.0%) and hypophosphatemia (13.3%). Although reasonably well-tolerated, this phase II study of panobinostat and bevacizumab in recurrent GBM did not meet criteria for continued accrual and the GBM cohort of the study was closed. In the recurrent AG cohort, the PFS6 rate was similar to historical controls. Updated data will be presented.